Differential axle assemblies are well known structures that are commonly used in many vehicles. Such axle assemblies include beam or rigid axles as well as axles in vehicles with independent suspension. The typical differential is made up of a centralized carrier/housing assembly, to which axle tubes are directly or indirectly attached. The gears are housed in a portion of the differential housing called the differential carrier. Two main configurations of axle housings are commonly used. One configuration is of unitized construction and has a differential carrier integral to the center section of the differential housing. The axle tubes are directly attached to this carrier/housing. This type is commonly referred to as the carrier type, or also as the Spicer or Salisbury type. A second configuration employs a separable carrier unit to house the differential gears, with the entire gear and carrier assembly being removable as a unit from the front of the axle housing. This type is commonly referred to as the banjo or front-loader type. The unitized differential axle assembly includes an access opening in the rear of the housing for the insertion of the differential gearing and other components. This access opening is closed with a bolt fastened cover after the components have been installed the housing.
The typical differential axle assembly includes many gears and other parts to transmit the rotational force of the engine to the drive wheels of the vehicle. This is accomplished by connecting the differential between the drive line input or drive shaft, and a pair of output shafts or axles that extend to the drive wheels. The drive line or drive shaft assembly, is connected by affixing the rear universal joint to the differential at the drive line connection point. The drive line connection point typically consists of a pinion yoke or a pinion flange. The yoke or flange is non rotatably affixed to the input shaft or drive pinion gear by mating an internally splined portion of the flange or yoke to an externally splined portion of the drive pinion gear. The flange or yoke is then axially retained by a bolted connection. The drive pinion gear and pinion flange or pinion yoke assembly is rotatably mounted within the front portion of the differential carrier and the flange or yoke protrudes therefrom. The drive pinion gear transmits rotational force to the other parts of the differential assembly in a manner well known in the art.
Known differential axle assemblies have certain drawbacks associated with the current configurations. For example, it has been found that high loads and frictional forces encountered by the internal components of the differential generate a great deal of heat. The lubricating oil within the differential facilitates reducing the friction, and to some degree aids in cooling the components by conducting heat away from the surface of the internal parts. During normal operation of the vehicle, the dynamic internal parts of the differential propel the lubricant oil onto the inside surfaces of the differential housing. Heat is conducted from the oil to the differential housing and transmitted to the atmosphere through radiation and convection. During severe duty and high load conditions, such as might be encountered while towing a trailer, ascending steep inclines or many other situations, the lubricating oil may become excessively hot. The natural radiation and convection may not sufficiently cool the lubricant oil, causing the oil to break down and lose viscosity. Once in this condition, the oil cannot lubricate as needed. This causes the friction between the internal parts to increase and generate more heat, furthering the destructive cycle that ends in mechanical failure of the differential.
Therefore, improved cooling of the differential axle assembly, and the lubricating oil therein, would be desirable. Previous attempts to provide cooling in a differential have employed remote oil coolers that allow fluid communication between the housing and a separate cooler. These often require extensive modifications to the differential housing. Other methods include modifying the differential housing or internal parts to promote better cooling through altered fluid flow. This method usually requires complete redesign of the internal differential components to include a pump or alternate oil passages. The use of cooling fins on the housing or cover has also previously been employed. Many of these modifications are costly to produce and difficult or impossible to install on existing differential axle assemblies, and others are not efficient enough to remove the desired amount of heat from the differential.